Sulfoxonium Ylide Chemistry. VIII. A Novel Rearrangement of Dimethylsulfoxonium Ylides

Reduction of dimethylsulfoxonium 3-ethoxycarbonyl-1-[1,2-bis(methoxycarbonyl)vinyl]-2-phenylallylide (1) and dimethylsulfoxonium 3-ethoxycarbonyl-1-[2-(ethoxycarbonyl)vinyl]-2-phenylallylide (5) with zinc in acetic acid gave (Z)- and (E)-3-methoxycarbonyl-4-ethoxycarbonyl-5-phenyl-3,5-hexadienoic acid methyl ester (6a and 6b), and (Z)- and (E)-4-ethoxycarbonyl-5-phenyl-3,5-hexadienoic acid ethyl ester (7a and 7b), respectively, whose structures were determined by the NMR spectral data and further chemical transformations. The reaction mechanism of the reductive rearrangement was proposed to proceed through an anion radical to form a four membered intermediate (11), which cleaved to non-conjugated dienes leading to Z and E conjugated products.